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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5817_Библиотеки_им_академика_М_И_Перельмана.pdf
Indications for Obstetric Ultrasound
2
Growth Restriction
왘 Definition: Infants with biological measurements
or birth weight below the 10th percentile.
왘 Incidence: About 10% of all live births. Preponder-
antly seen after high-risk pregnancies, such as status post retarded infant, PIH, maternal illness, or in
multiple pregnancies.
왘 Prognosis: Perinatal mortality and morbidity of
growth-restricted children increases significantly.
While somatic delays are usually caught up in the
first year of life, neurological development may be
delayed into the second year of life.
왘 Types: Growth restriction includes symmetrical
(type I) and asymmetrical (type II) retardation.
However, all possible combinations of “mixed
types” can occur, depending on the onset and severity of the growth delay.
− Symmetrical retardation: ca. 20−30% of all re-
tardations. Onset in the second trimester. Mainly
affects children who are genetically small or
children with diminished growth potential due
to chromosomal or structural disorders, or damage by toxic exogenous agents or infections
F
8.6a).
ig.
(
− Asymmetrical retardation: ca. 70−80 % of all re-
tardations. Onset in the second to third
trimester. The main cause is inadequate
nutritional supply due to placental insufficiency.
Another sonographic indication might be reduced amniotic fluid (Fig. 8.6b).
왘 Clinical procedure: Once a restriction has been de-
tected, it should be monitored by means of regular
biological measurements. We recommend a minimum interval of 10 days. If the interval is shorter,
the measuring error can be greater than actual
growth. In an early symmetric growth restriction a
comprehensive workup for malformations and if
necessary karyotyping is strongly recommended.
Since viral infections can also lead to growth restriction, serology (TORCH syndrome) can be a valuable tool.
In what follows we give details on the individual indications for using Doppler ultrasound in obstetrics.
94
Suspected IUGR
Such suspicion is raised by sonographic biological
measurements. The question is: How much delay in
fetal growth can be defined as restricted growth? In
general growth restriction is defined by biological fetal
measurements, especially abdominal girth, below the
fifth percentile. The measurement must refer to the
correct gestational age, determined during the first set
of measurements taken during the first trimester. The
best and most precise measure of gestational age is the
crown−rump length taken during the first trimester.
It is important to remember that every biological
measurement is subject to error. In order to ensure a
broad indication for Doppler ultrasound, and not to
overlook infants with IUGR or abnormal Doppler findings, the measure for IUGR may be referred to the 50th
percentile. By using this percentile, delays of two
weeks or more may be seen as an indication for Doppler sonography. This ensures that every growth restriction will be detected.
Since the authors are certainly conscious of the
problem posed by such a broad indication, the
dilemma faced by the obstetric practitioner may be
clarified by a practical example: For a neonatologist a
normally developed, healthy newborn, delivered at the
calculated term with a weight of 2500 g, has a normal
birth weight. The obstetric practitioner, however, sees
this child before delivery by ultrasound as below expected weight. He now faces the dilemma of managing
labor while uncertain about the infant’s ability to
withstand it.
In determining the biological measurements, gestational age at which they were made must be noted.
Experience shows that there are two gestational periods during which IUGR is either problematic or evident. The condition is problematic when the fetus
shows clear signs of growth restriction in the 26th to
28th week of gestation, while IUGR evident after the
30th week of gestation as a rule no longer poses an obstetric problem. It is important to note clinical signs of
retarded development, since some guidelines only require a third ultrasound examination after the 29th
week of gestation.
Examination of the maternal vessels (uterine aa.)
will determine if the cause of an IUGR is primarily
uteroplacental insufficiency (in which case Doppler
examination will show abnormal maternal vessels) or
fetoplacental insufficiency (normal flow in maternal
vessels). The risk for the infant can, however, only be
estimated with certainty by examining the fetoplacental and fetal vessels. If these display a normal perfusion
pattern, the insufficiency demonstrated by biometry is
compensated, while an abnormal finding indicates an
uncompensated insufficiency.
Thus, when biological measurements demonstrate
placental insufficiency, a Doppler examination can
make the distinction between a compensated and an
blubber
Fig. 8.6a Characteristic curve
of symmetrical fetal growth restriction (upper curve: biparietal
diameter [BPD]; middle cur ve:
femur length [FL]; lower curve:
thoracic diameter [TD]).
BPD
mm
110
100
90
80
70
60
50
40
30
20
10
a
Suspected IUGR
FL
10 12 14 16 1 8 2 0
2286 24262830323436384042
Implantation site
BPD
FL
TD
22861012141618
24 26 28 30 32 34 36 38 40 4220
BPD
FL
mm
110
100
90
80
70
60
TD
110
mm
100
90
80
70
60
50
40
30
20
10
Obstetric Applications of Doppler Ultrasound
Fig. 8.6b Characteristic curve
of asymmetric fetal growth restriction (upper curve: biparietal
diameter [BPD]; middle cur ve:
femur length [FL]; lower curve:
thoracic diameter [TD]).
BPD
mm
110
100
90
80
70
60
50
40
30
20
10
b
FL
10 12 14 16 1 8 2 0
24 26 28 30 32 34 36 38 40 42
2286
Implantation site
BPD
BPD
FL
mm
110
100
90
FL
80
70
60
TD
110
TD
mm
100
90
80
70
60
50
40
30
20
22861012141618
24 26 28 30 32 34 36 38 40 4220
10
blubber
95
Indications for Obstetric Ultrasound
2
uncompensated condition. Intrauterine growth restriction can therefore be regarded as an attempt at
compensation. Delay in fetal growth is a response to
reduced nutritional supply from the placenta. While
the smaller infant is able to survive on the reduced
supply the system is in balance. This consideration ex-
PIH/Preeclampsia/Eclampsia
The basis for the maternal condition is a placental disorder, which can induce a rise in blood pressure. The
elevated blood pressure, and especially elevation of the
diastolic pressure, may lead to further reduction in
placental perfusion. Since the blood pressure elevation
is frequently chronic, this problem often leads to fetal
IUGR. For this reason it is necessary to determine
whether the infant is suffering from a chronic lack of
blood supply in cases of maternal hypertension. Of
course, in such cases, too, the diagnosis rests on fetal
biological measurements.
If the blood pressure elevation is acute, it may not
manifest itself in changes in the Doppler parameters of
the fetal vessels. In such cases special attention must
be paid to the cardiotocogram (CTG).
Demonstration of a notch in the examination of the
maternal vessels during the third trimester is charac-
plains why our studies show that for a growth delay of
abdominal girth of two weeks referred to the 50th percentile, fewer than 5% of cases display abnormal findings in the fetal aorta or umbilical aa. by Doppler sonography, while for a delay of five weeks or more we
found 40−50 % abnormal values.
teristic of chronic blood pressure elevation. Since,
however, the pressure rise in such cases will already
have been detected during regular monitoring of blood
pressure, the examination of maternal vessels is redundant. Rather, in this case Doppler sonography must
be used to evaluate the condition of the infant by examining the fetoplacental and fetal vessels.
By contrast, Doppler ultrasound of the maternal vessel plays an important role in the f irst and second
trimesters. A defective trophoblast invasion, which
might cause toxemia, is characterized by a persisting
rise in resistance—especiallya notch—in the uterine aa.
Hence Doppler sonography of the uterine aa. in the
first and second trimesters acquires prognostic significance for the future course of the pregnancy.
96
Status Post Dysmature Delivery/Intrauterine Death
After the delivery of a dysmature infant it is desirable
in the next pregnancy to exclude a uteroplacental insufficiency as early as possible, or, if it is already established, to treat it with 100 mg acetylsalicylic acid (ASA)
and close supervision.
An impending risk of placental insufficiency can be
evaluated with the help of Doppler sonographic examination of the uteroplacental vessels during the second trimester. Hence where there is a history of dysmaturity, the uterine aa. should be examined in the
second trimester, so that at the first sign of uteroplacental insufficiency therapy with ASA and close supervision may be initiated.
Admittedly there are cases of dysmaturity that are
accompanied by normal uterine perfusion and only be-
come apparent in fetal growth restriction. Similarly, intrauterine death resulting from an acute event cannot
be predicted by Doppler ultrasound.
The indication “status post intrauterine fetal death”
carries with it a number of problems. Above all else the
cause of a previous intrauterine death must be established. Should this be due to an acute event, such as a
cord looped around the neck or abruption placentae,
an increased risk of a similar event cannot be determined by Doppler ultrasound. Evidence that an IUGR
may again be present can only be evaluated by biological measurement when fetal death is a result of chronic
placental insufficiency. The risk to the subsequent gestation may then be evaluated by adding Doppler
sonographic examination.
blubber
Status Post Preeclampsia/Eclampsia
Reasonable Suspicion of Fetal Anomalies or Fetal Disease
The same considerations as those listed under PIH are
valid for this indication. To assess the risk of again
developing eclampsia, the maternal vessels can be examined in the first and second trimesters, to display
the proper development of placental perfusion, and so
placental maturation, or to detect any abnormalities.
Therapy may be initiated with ASA. Biological
Abnormalities in the Recorded Fetal Heart Rate
This relates in particular to an abnormal CTG.
Experience suggests that a Doppler sonogram that is
abnormal due to chronic placental insufficiency may
be recorded 10−16 days before an abnormal CTG.
Granted, an abnormal CTG does not necessarily follow
an abnormal Doppler sonogram, but may be expected
with a probability of about 60 %. The more abnormal
the sonogram, the more likely it is to be followed by
the appearance of an abnormal CTG.
An abnormal CTG rests on a different pathological
basis than an abnormal Doppler ultrasound finding.
Should the CTG be abnormal because of an acute event,
such as an umbilical cord looped around the neck, an
measurement can uncover any fetal IUGR due to
chronic changes in the placenta. Doppler sonographic
examination of the fetal vessels in the third trimester
to follow the condition of the fetus will then show how
the infant is coping with the placental or maternal disorder.
abnormal Doppler finding is not to be expected. On the
other hand, if the abnormal CTG derives from a chronic
placental insufficiency, the Doppler findings are also
likely to abnormal, since as a rule, as noted above, it
precedes the CTG in such cases.
Clinical management differs correspondingly. If the
CTG and Doppler are both abnormal, the infant is likely
to be growth restricted and termination of pregnancy
is often necessary. This is not necessary if the CTG is
abnormal, but acceptable, and the Doppler findings are
normal. In such cases Doppler ultrasound is not helpful
in guiding management.
Obstetric Applications of Doppler Ultrasound
Reasonable Suspicion of Fetal Anomalies or Fetal Disease
The suspicion of anomalies is an important indication
for Doppler ultrasound for two reasons. Firstly, Doppler ultrasound demonstrates and evaluates the malformations (e.g., renal agenesis can usually only be demonstrated by the absence of a renal a.). Secondly, infants with malformations are often growth restricted,
and must therefore be monitored with Doppler ultrasound, since it is especially important for infants with
malformations to be delivered at maturity, in order to
improve their tolerance for any postpartum treatments
that may become necessary. There are also malformations, such as omphalocele, where biological measurement of the abdomen is not sufficient to show normal
development. In such cases Doppler ultrasound can assist in monitoring the infant’s condition, since the fetal
vessels can indicate whether the infant’s blood supply
is or is not adequate.
Multiple Pregnancy with Discordant Growth
While multiple fetuses are normally expected to show
diminished growth, discordant growth in multiple fetuses is an important sign that the infants must be
monitored intensively in utero. In such cases examination of the fetal vessels for monitoring purposes is extremely important. The selection of vessels poses a
problem. Uterine vessels do not allow conclusions to
be drawn about the infants, and especially in the third
trimester the umbilical vessels cannot be assigned to a
specific infant. In these cases the fetal aorta must be
considered the most important vessel. However, many
authors regard not only discordant growth but the demonstration of growth restriction as an indication for
Doppler ultrasound.
97
blubber
Indications for Obstetric Ultrasound
Suspicion of Cardiac Anomaly or Heart Disease
2
It is axiomatic that clinically no cardiac anomaly can be
discovered by Doppler sonography of peripheral fetal
vessels. Rather, fetal cardiac anomalies are detected as
part of a general investigation for malformations using
gray-scale sonography. Color Doppler and spectral
Doppler examinations are only introduced to clarify
the extent of the defect or cardiac function. As previously noted, as a rule these cases must be brought
close to term, in order to be delivered as close to maturity as possible. Doppler ultrasound helps in managing
such cases.
Other Indications
Other indications for Doppler ultrasound have been
proposed. These include preexisting maternal illnesses
relating to the blood vessels such as hypertension, nephropathies, diabetes mellitus, autoimmune diseases,
and clotting disorders. All these diseases can result in
placental insufficiency by causing impaired placental
maturation or trophoblast invasion. Biological
measurements and Doppler ultrasound can detect risk
in such cases in a timely manner. In particular we want
again to point out that in the future, examination of the
uterine vessels during the first and second trimesters
may put at our disposal a parameter that can predict
the risk of developing placental insufficiency in the
third trimester.
We should also point out that in a poorly regulated
diabetic pregnant woman an infant of normal size may
represent a relative restriction, since in such a case the
infant would be expected to be overweight. Thus, in
this situation an infant of normal weight represents an
indication for Doppler sonography.
Summary:
Indications for Doppler Ultrasound in the First, Second, and Third Trimesters
98
First Trimester
So far there is no definite indication for Doppler ultrasound in the first trimester. Changes specific to pregnancy can be studied by examining the uterine aa.,
perhaps leading to early detection of an abnormal gestation. Very rare fetal anomalies may be detected
early with the use of color-coded Doppler ultrasound,
for example, multiple pregnancies with acardia or
thoracopagus. Note that Doppler examination of the
embryo involves the transmission of a high degree of
energy and that therefore the indication for such an examination in the first trimester must be robust.
Second Trimester
Research has shown that Doppler sonographic examination of the uterine aa. can detect portents of the future development of complications of pregnancy such
as hypertension or preeclampsia. In the main this is
seen in a postsystolic notch, which may be considered
a Doppler sonographic correlate of a defective trophoblast invasion after the completion of the second trophoblast invasion, making screening possible. The in-
complete maturation of the placenta elicits a cascade
of events that results in the above-mentioned complications.
Additionally, color Doppler ultrasound is an important diagnostic tool for assessing and evaluating fetal
anomalies.
Third Trimester
During the third trimester the first consideration is the
condition of the infant. Correspondingly the examination of the fetal or fetoplacental vessels is of prime importance.
Abnormal Doppler findings are significantly associated with a pathological course of the pregnancy.
Examination of the umbilical aa. and the fetal aorta
provides important information about the condition of
the fetus. If the result is abnormal, examination of the
the risk. Doppler sonography of the fetal v.’s may at
times allow an even more precise evaluation of the
fetal risk.
Doppler ultrasound can be helpful in diagnosing
fetal anomalies in the third trimester as well.
blubber
9 Doppler Sonography in Obstetrics—Screening At-Risk
Populations
The purpose of Doppler screening is to separate an at-
risk group from the total population of pregnant
women for further diagnostic studies, more intensive
monitoring, and treatment. The goal is to improve obstetric results when compared to an unexamined
population. However, before establishing a Doppler
screening program we must assess the diagnostic and
clinical validity of the Doppler technique.
The diagnostic validity of Doppler ultrasound in obstetrics may be measured by the reliability with which
an abnormal Doppler finding is associated with an abnormal pregnancy as determined by research studies.
The statistical criteria for diagnostic validity are the
sensitivity and specificity of a test. The sensitivity of a
test indicates how many abnormal cases are identified
correctly (true positive/[true positive + false negative]).
The specificity of a test indicates the proportion of
genuinely healthy individuals in a test cohort (true
negative/[true negative + false positive]). This implies
that healthy individuals may be falsely classified as
diseased, while genuinely diseased individuals may
not be recognized. A good screening test should be
easy to perform, cost-effective, noninvasive, and effective. One hundred percent sensitivity and specificity is
an unattainable ideal in medicine (Table
Tab. 9.1 Test evaluation
Actual Test
Positive Negative
Positive TP FN
Negative FP TN
TP = True positive
TN = True negative
FP = False positive
FN = False negative
9.1).
Important statistical concepts
Sensitivity: TP/(TP + FN)
Specificity: TN/(TN + FP)
Negative predictive value: TN/(TN + FN)(TN rate)
Positive predictive value: TN/(TP + FP)(TP rate)
Efficiency: (TP +TN)/n
Prevalence: (TP + FN)/n
Obstetric Applications of Doppler Ultrasound
Validity of a Test
A suitable way to test the robustness of several indices
is to compare their test validity. A tried and tested way
of performing such a comparison is to construct a relative (receiver) operating characteristic (ROC) curve. For
this purpose the sensitivity and specificity for a number of diagnostic threshold values are calculated and
plotted. The ordinate represents the sensitivity from 0−
100%, the abscissa the specificity from 100−0 %. The
curves are constructed by selecting five to six threshold values from both the normal and abnormal range
of the test used. Any point on such a curve represents
both the sensitivity and the specificity at that point.
The maximal perpendicular distance of the curve from
the diagonal of the diagram (line of chance) is a
ig. 9.1). The curve
measure of the validity of the test (
the curve to the diagonal of the diagram is a measure of the
validity of the test.
F
blubber
컄Fig. 9.1 ROC curve. The maximal perpendicular distance from
Sensitivity
100
80
60
40
20
0
100
80
60
40
20
Specificity
0
99
Doppler Sonography in Obstetrics—Screening At-Risk Populations
2
of a test shows the increase in sensitivity in its ascending part, coincident with the decline in specificity. In
the horizontal part any increase in sensitivity results in
an ever larger loss of specificity. The apex of the curve
represents the optimal validity of the test, since here
maximal sensitivity coincides with maximal speci-
Validation of Indices
Sensitivity
100
50
0
100
a
Sensitivity
100
50
50
Specificity
PI of umbilical a.
RI of umbilical a.
A/B ratio of umbilical a.
0
ficity. If the curves of different tests are entered into
the diagram, the different tests can be compared ob-
jectively (validation). The curve with an apex closest to
the upper left hand corner of the diagram represents
the superior test.
The criterion for validity we selected is the predictive
value of Doppler flow rates for a subsequent abnormal
cardiotocogram (CTG). We compared the validity of
readings from the umbilical a. and the middle cerebral
a. (MCA) to the pulsatility index (PI), resistance index
(RI), and ratio of systolic peak to end-diastole (A/B
ratio) and the corresponding ratios (MCA/aorta) (
9.2,9.3).
In Figure 9.2a the curves for the index threshold
values of the umbilical a. show an equal increase in
sensitivity with little loss of specificity for all indices.
In the more distal portions of the curves they separate
and form distinct apices. Although these lie close together, the greatest distance is that of the PI for the
umbilical a.
Figure 9.2b the ROC curves for the indices of the
In
MCA lie close together throughout. No index is visibly
superior. However, in respect of validity the MCA is
clearly inferior to the umbilical a.
By a similar process we can test whether the ratio of
the PI of the MCA to the PI of the aorta can provide
greater accuracy. The curve in Figure 9.3 shows—at
least for the current search—that the ratio is the superior measure. This finding expresses the pathophysiological assumption that the CTG is the end point of a
developing condition. The shift of circulation to the
brain in chronic placental insufficiency is a compensatory mechanism, which can be recognized in the
Doppler sonogram before an abnormal CTG indicates
that the fetal circulation is beginning to fail.
Resolving the cost−benefit ratio leads to clinical sig-
nificance, i. e., it determines whether adding information from Doppler ultrasound can lead to clinical
measures that will improve obstetric outcome. Controlled prospective randomized studies using two
treatment groups were undertaken to clarify this issue.
In one group conventional criteria were used (control
group), while the other introduced results from Doppler ultrasound into treatment decisions.
Figs.
100
0
100
PI of MCA.
RI of MCA.
A/B ratio of MCA.
b
50
Specificity
blubber
0
컅 Fig. 9.2 Comparison of test validities by means of ROC curves.
Criterion for the predictive ability of the test is the prediction of
an abnormal CTG by Doppler flow values. (a) Readings from the
umbilical a. (b) Readings from the MCA.
Screening in Cases of Suspected Uteroplacental Perfusion Disorders and/or Pregnancy-Induced
Fig. 9.3 Comparison of test validities by ROC curves. The curve
tests whether the ratio PI aorta/PI MCA increases precision in
answering the questions posed in Fig
9.2.
Sensitivity
100
50
0
100
PI of umbilical a.
PI of MCA/PI aorta
PI MCA.
50
Obstetric Applications of Doppler Ultrasound
0
Specificity
Screening Population
It is easy to answer the question of whether screening
by Doppler ultrasound is valuable as a general screening tool (Doppler for all pregnant women) or if it
should be used exclusively for at-risk populations.
While in mass screenings the cost−benefit ratio is significantly shifted to the unprofitable side, Doppler intervention in at-risk groups is useful. Guidelines that
establish the place of Doppler ultrasound in obstetrics
use a list of indications that are based on risk factors
determined by physical findings and/or clinical history
(cf.
Chap
8, p. 91). The controversy over the un-
ter
favorable acoustic intensity of pulsed wave (PW) Doppler instruments and over the clinical relevance of the
results led to restriction of their use to the second half
of pregnancy.
Screening in Cases of Suspected Uteroplacental Perfusion Disorders and/or Pregnancy-Induced Hypertension
The list of indications for Doppler ultrasound in these
conditions includes risk factors derived from both
physical examination and history:
− Pregnancy-induced hypertension (PIH)/preeclam-
psia
− Status post preeclampsia/eclampsia
− Collagen diseases (e.g., systemic lupus er ythemato-
sus)
− Severe diabetes
− Suspected intrauterine growth restriction (IUGR)
− Fertility problems
− Status post habitual abortion/stillbirth
− Late primipara
A postsystolic notch in the uteroplacental flow
waveform that persists or recurs in the second half of
pregnancy indicates abnormal reflection of the pulsed
wave from the spiral aa. due to a defective trophoblast
invasion. The latter indicates poor adaptation of the
uteroplacental vascular bed to the needs of the fetus,
leading to regressive changes in the vessels and a resulting increase in resistance. The notch may be found
on one or both sides. A unilateral placental implantation has additional prognostic implications. Abnormal
indicators of resistance and a notch, by their association with dystocia or premature delivery, are clearly
better indicators than previous long-established parameters such as uric acid level, creatinine clearance, and
retinal changes (grades 1−3).
The last link in the chain of evidence in determining
diagnostic significance lies in a highly significant correlation between uteroplacental perfusion disorders de-
101
blubber
Doppler Sonography in Obstetrics—Screening At-Risk Populations
2
tected by Doppler ultrasound and histomorphological
pathology of the vessels in the placental bed (sensitivity: 94 %; specificity: 86%) (Voigt et al 1992).
To test the clinical significance of Doppler ultrasono-
graphy of the uteroplacental bed, the use of acetylsali-
cylic acid (ASA) following an abnormal Doppler reading was compared with placebo in a controlled therapeutic trial. A significant reduction in hypertensive
complications of pregnancy, including the rate of cesarean section, was achieved in the ASA group.
Screening for Suspected Fetoplacental Perfusion Disorders and/or IUGR
The list of indications for these disorders also includes
indicators of risk derived from physical examination
and history. It is congruent with the initial criteria used
above in suspected uteroplacental perfusion disorders.
The most important risk indicator is finding fetal
measurements two to three weeks below the median
value of the curve plotting fetal weight against the determined fetal age. The lack of precision in estimating
Time interval abnormal Doppler –
abnormal CTG
%
70
60
50
40
30
20
10
0
Normal < 1 1-2 3- 5 6 -10 11-30 31-50 Days
Fig 9.4 Time interval between an abnormal Doppler reading
and an abnormal CTG.
gestational age and fetal weight brings two possible errors to daily clinical practice, suggesting that it would
be safest to extend the indications as widely as
possible.
End-diastolic zero flow in the umbilical aa. is considered to be the most reliable sign of insufficient intrauterine blood supply. Abnormal Doppler findings in
the umbilical aa. correlate closely with IUGR, abnormal
CTG, cesarean sections for hypoxia, neonatal acidosis,
and depression, the duration of intensive neonatal
treatment, and the histopathology of the placenta (di-
agnostic significance). Zero or reverse flow in the
umbilical aa. combined with abnormal Doppler findings in the MCA led to an increase in later neurological
abnormalities.
Randomized, prospective, controlled studies of management for IUGR address clinical significance. The re-
duced frequency of emergency cesarean sections and
sections for fetal hypoxia speaks for the improved information available to the obstetric attendant. Depending on whether an outpatient or inpatient population
was studied, the lead time over CTG in obtaining information leading to delivery was 3 to 10 days, in extreme
cases 40 days. The fear that the procedure might lead to
iatrogenic premature delivery or an increased rate of
cesarean sections was found to be groundless (
Fig.
9.4).
102
Summary
Doppler ultrasound is a useful additional monitoring
technique for high-risk pregnancies, especially for PIH
and growth restriction. As a long-term indicator it is
better than the CTG, while in the short term it provides
early warning of the potential for intrauterine oxygen
deprivation. It is not so much suitable for the diagnosis
of IUGR as for the evaluation of risk after growth restriction has been diagnosed by fetal measurement.
If the indications for the use of Doppler ultrasound
blubber
are clear and not too narrowly set, they will usually
lead to an examination of both areas of perfusion, the
uteroplacental and the fetoplacental bed. If the findings are abnormal, or if diagnostic studies are expanded to exclude other conditions, this will be followed by examination of the fetal vessels (abdominal
aorta, MCA, fetal v.’s). Clinical conclusions should only
be drawn if the results are congruent with those of
other methods.
10 Doppler Ultrasound Diagnosis in Preeclampsia,
Eclampsia, and HELLP Syndrome
The Working Group on High Blood Pressure in Pregnancy classifies hypertensive disorders in pregnancy
as follows:
왘 Preeclampsia/eclampsia: Occurs after the 20th
week; increased bood pressure (gestational hypertension) with proteinuria. Eclampsia adds tonic/
clonic seizures. HELLP syndrome: hemolysis, elevated liver enzymes, low platelet count;
왘 Chronic hypertension: primary or secondary;
왘 Preeclampsia superimposed on chronic hyperten-
sion;
왘 Gestational hypertension (only during pregnancy):
Elevated blood pressure occurring after the 20th
week of pregnancy that lasts no longer than six
weeks postpartum. Proteinuria is absent;
왘 Transient hypertension (only after pregnancy).
‘Toxemia’ of pregnancy has been known since antiquity. The disease does not present a uniform clinical
picture and its causes and pathogenesis have not been
clearly defined to date. No doubt immunological
changes play an important role. The vessels show constriction that interferes with blood flow. Vascular damage leads to subendothelial deposition of thrombocytes and fibrinogen. Ensuing disturbances in the microcirculation may eventually lead to the disseminated
intravascular thrombosis of the HELLP syndrome. The
term pregnancy-induced or gestational hypertension
(PIH) was introduced to describe the principal symptom.
The endothelium probably plays a significant role in
the pathophysiology of gestational hypertension
(McCarthy et al. 1993, Roberts et al. 1981, Taylor and
Roberts 1991). The production of prostacyclin, which
acts as a vasodilator, is reduced in the endothelium,
(Goodman et al. 1982, Mäkilä et al. 1984, Walsh 1985),
while vasoconstrictive endothelin is increased (Nova et
al. 1991). Additional nitrogen monoxide (NO), an endothelium-derived relaxing factor (EDRF), is probably
an important factor in the genesis of gestational hypertension. The corresponding endothelial changes can be
demonstrated morphologically (Furchgott and Zawadski 1980, Palmer et al. 1987, Pinto et al. 1991, Roberts et
al 1981). Beinder and Lang (1994), using a laser Doppler flow meter, were able to show changes in the reactivity of the microcirculation in toxemic patients.
There is a fundamental change in hemodynamics
during pregnancy. Partly this is due to the greatly dilated vascular bed. Total peripheral resistance can be
observed to decrease considerably during the 14th to
24th week of pregnancy. The resistance then rises
again slowly until the end of pregnancy to normal
values similar to those found prior to pregnancy. An
exception is renal perfusion, which has been found to
rise steadily until the end of pregnancy.
In contrast to this normal course, during preeclampsia and eclampsia vascular resistance increases significantly as described above. This rise reduces perfusion and is responsible for the symptoms of preeclampsia.
Obstetric Applications of Doppler Ultrasound
Pathological Changes in Preeclampsia
Over time numerous hypotheses for the development
of preeclampsia have been developed, based on its
three cardinal symptoms, namely edema, proteinuria,
hypertension (EPH) and the observation that it is often
associated with fetal growth restriction.
The changes based on the most robust observations
may be summarized as follows:
왘 Decreased perfusion of uterus and kidney,
왘 Reduced glomerular filtration rate,
왘 Increased vascular sensitivity for angiotensin II,
왘 Reduced urine output after sodium loading,
왘 Glomerular changes,
왘 Fibrin monomers dissolved in the plasma.
blubber
Plethysmographic studies found significant elevations
in the total peripheral resistance in preeclamptic
patients. This is the expression of contraction of the
vascular musculature in the peripheral resistance system and a decrease in the resistance of the venous bed.
A number of symptoms can be ascribed to this vascular
Fig.
spasm (
The cause of the vasoconstriction and salt retention
is considered to be the heightened sensitivity to angiotensin II, added to the decreased production of prostacyclin. The effects of prostacyclin include vasodilatation and inhibition of thrombocyte aggregation.
Moreover, the fluid properties of the blood are altered
by increased aggregation of erythrocytes and plasma
10.1).
103